There has heretofore been known a seamless can (can having no seam on the side surface) formed by subjecting a resin-coated metal sheet to the draw working, bend-elongation working (stretch working) and/or ironing working, the resin-coated metal sheet being the metal sheet such as aluminum plate, tin plate or tin-free steel plate coated with an organic film.
As methods of coating the seamless can with an organic film, further, there have been known a method of applying an organic coating material onto a can after it has been formed, and a method of laminating a resin film such as of a thermoplastic polyester on a metal sheet of before being formed into a can and use the resin-coated metal sheet.
To form a seamless can from the resin-coated metal sheet, it is necessary to satisfy such requirements as close adhesion of the resin coating during the working, shock resistance, flavor-retaining property and corrosion resistance. From the above standpoint, therefore, there has heretofore been used a resin-coated metal sheet that is coated with an isophthalic acid-containing polyethylene terephthalate (patent document 1).
In forming the seamless can, the ironing working is conducted and, thereafter, the trimming working is conducted to shear and cut an upper part of the can body portion by holding the can body portion with a can body inner cutter and a can body outer cutter that rotate, respectively. At the timing of the trimming working, it is required that the resin coating is well sheared and cut together with the metal sheet. At a lower portion of the can body portion, further, the can comes in contact with a conveyer guide or the cans come in contact with one another, and the resin coating on the outer surfaces is burred. In case the printing is made on the burred portion, the printed ink is peeled off as the burred portion undergoes the thermal shrinking, and appearance becomes defective (hereinafter, the phenomenon of ink peeling is often called “abrasion”).
In recent years, further, the cans have been sold bearing a prize seal called “tack seal” that is stuck to the surface of the can body portion accompanied, however, by a problem in that the printed ink is peeled off at the time when the seal is removed and a problem in that a foamed ink that is used in an attempt to improve decorative effect on the outer surface is peeled off if the cans come in contact with each other or are rubbed by each other during the transit. Therefore, it has been desired to further improve the close adhesion of the printing ink.